To examine the role of development in the origin of evolutionary novelties, we investigated the developmental mechanisms involved in the formation of a complex morphological novelty-branched feathers. We demonstrate that the anterior-posterior expression polarity of Sonic hedgehog (Shh) and Bone morphogenetic protein 2 (Bmp2) in the primordia of feathers, avian scales, and alligator scales is c...

While the ventralizing factor Sonic hedgehog is expressed in the entire notochord (Development 121 (1995) 2537) the latter displays distinct ventralizing activities along its rostrocaudal axis. Hence, in HH stage-10 chicken embryo, the caudal notochord exhibits floor plate inducing capacities lost by rostral regions (Development 117 (1993) 205). Therefore, we hypothesize that the caudal notocho...

The thalamus is a central brain region that plays a crucial role in distributing incoming sensory information to appropriate regions of the cortex. The thalamus develops in the posterior part of the embryonic forebrain, where early cell fate decisions are controlled by a local signaling center - the mid-diencephalic organizer - which forms at the boundary between prospective prethalamus and tha...

Sonic hedgehog (Shh), which regulates proliferation in many contexts, functions as a limb morphogen to specify a distinct pattern of digits. How Shh's effects on cell number relate to its role in specifying digit identity is unclear. Deleting the mouse Shh gene at different times using a conditional Cre line, we find that Shh functions to control limb development in two phases: a very transient...

Each vertebrate species displays specific tooth patterns in each quadrant of the jaw: the mouse has one incisor and three molars, which develop at precise locations and at different times. The reason why multiple teeth form in the jaw of vertebrates and the way in which they develop separately from each other have been extensively studied, but the genetic mechanism governing the spatial pattern...

Ecological explanations have been put forward to account for the precocious or delayed development of patency in ducts leading to the vomeronasal organ (VNO) in certain mammals. Perinatal function may be related, in part, to the patency or fusion of the vomeronasal and nasopalatine (NPD) ducts. However, few studies have focused on NPD development in primates, which generally have a prolonged pe...

Sonic hedgehog (Shh) is thought to control the generation of motor neurons and interneurons in the ventral CNS. We show here that a Shh-independent pathway of interneuron generation also operates in the ventral spinal cord. Evidence for this parallel pathway emerged from an analysis of the induction of ventral progenitors that express the Dbx homeodomain proteins and of Evx1/2 (V0) and En1 (V1)...

Axial patterning of the embryonic brain requires a precise balance between canonical Wnt signaling, which dorsalizes the nervous system, and Sonic hedgehog (Shh), which ventralizes it. The ventral anterior homeobox (Vax) transcription factors are induced by Shh and ventralize the forebrain through a mechanism that is poorly understood. We therefore sought to delineate direct Vax target genes. A...

Hedgehog (Hh) signalling plays an important role in various developmental processes by activating the Cubitus interruptus (Ci)/Glioblastoma (Gli) family of transcription factors. In the process of proper pattern formation, Ci activity is regulated by multiple mechanisms, including processing, trafficking, and degradation. However, it remains elusive how Ci distinctly recognizes the strong and m...